Abstract:Using the grade response multilevel facets model(GR-MLFM),which formulated by Kang,Sun and Zeng(2016),to explore the impact of number of raters and number of items on the ability estimation.Results based on simulation show that:(1)with the increase of number of items,the correlation between estimates and true values become larger;(2)The main effect of both number of items and number of raterson MAB and RMSE are significant,also the interaction effect between these two variables is significant;(4)Post hoc analyses show that when the number of items are small,3 raters can lead to the best ability estimation; with the increase of the number of items,the error of estimates for 4 raters decreased dramatically,and yields the smallest errors.